This invention relates to apparatus for regulating the flow of a liquid being delivered to a patient such as in the administration of intravenous (I.V.) solutions, and more particularly to disposable flow regulation apparatus which will establish and maintain a rate of flow which will not be altered by changes in elevation of the point of administration, venous pressure, or the level of the supply liquid.
The administration of glucose, saline, or other solutions with or without pharmaceuticals to patients in hospitals or elsewhere is a common mode of treatment capable of fulfilling a variety of medical requirements. In a typical arrangement for such administration there is utilized a stand for supporting a reservoir containing a measured amount of the liquid, tubing extending down from the reservoir, and, for intravenous feeding, an implement which would include a needle attached to the end of the tube for delivering the liquid into the body of the patient.
The reservoir is ordinarily held well above the point of administration so that gravity is relied upon to provide the necessary pressure to insure continuous flow of the liquid. A valve in the tubing not only permits fluid flow to be initiated or terminated at will, but also regulates the rate of flow so that the nurse or other medical technician can set the rate of flow as prescribed by the attending physician. Customarily a drip chamber is provided to remove air and permit clear visualization of the rate of flow by counting the number of drops per unit of time.
In my U.S. Pat. No. 4,515,588 there is shown a regulator for such use which is capable of maintaining the selected flow rate of such solutions regardless of changes in fluid pressure caused by changes in head. In that patent, the drip chamber is relied upon to indicate the flow rate to be maintained.
The aforementioned patented device is made typically of six or more parts requiring assembly, and some of the assembly requires stretching of the membrane contained therein. Since the regulator is disposable, that is, it is disposed of after a single use, the number of parts involved and the complexity of the assembly produces a cost factor which in some situations could limit its availability.
Furthermore, when the patented regulator is put into use, the technician establishes the flow rate by turning the dial or knob on it until the desired drip rate is obtained in the drip chamber. The regulator uses a screw type metering valve which distorts a rubber diaphragm into a tapered orifice thus varying the orifice and metering the flow into the regulating chamber. The distortion is unpredictable and the control range can vary and some initial drift can even occur for a given setting of the control knob. As a result, it is not possible to establish a uniform calibration at the time of manufacture so that the dial can be set to read in terms of flow rate. In addition, since the diaphragm is put under stress by being stretched at the time of assembly, during the shelf life of the regulator its flow regulation characteristics can drift.
There are regulating devices on the market having numbers on their dial areas but these numbers are only valid for a specific head height. In fact, one such manufacturer has supplied a paper ruler with each device to facilitate setting the exact height required that will make the numbers indicated valid. Any change in this dimension voids the setting values. To make these numbers meaningful the fluid level must not change in the supply bag and the output end must not change position and the patient's venous pressure must not change.
In addition, a variety of other patented devices are concerned with the regulation of liquid flow.
In U.S. Pat. No. 3,783,892 there is shown a long timing fluidic device which employs either a spring with a diaphragm or multiple diaphragms to control fluid flow.
In U.S. Pat. No. 3,886,968 a flow control device is disclosed which utilizes a spring in combination with a diaphragm. The spring remains in contact with the diaphragm.
In U.S. Pat. No. 4,043,332 there is described a constant flow rate liquid medicament administering device which utilizes a diaphragm with a valve stem attached thereto and thereby loading the diaphragm.
In U.S. Pat. No. 4,316,460 a gravitational flow system is illustrated which employs a seated diaphragm which becomes unseated upon the application of the secondary liquid.
In U.S. Pat. No. 4,594,058 there is disclosed a single valve diaphragm pump using a diaphragm attached to a cylinder actuated by a magnetic solenoid.
In U.S. Pat. No. 4,604,090 is illustrated an implantable medication infusion device which utilizes a diaphragm having a magnet mounted thereon to adjust the diaphragm.
The above arrangements are all complex, expensive to manufacture and assemble, and in some cases there would appear to be the strong possibility that diaphragm characteristics can change substantially during shelf lives.